The present invention relates to a method and apparatus for the production of alloyed copper rod by continuous rod-casting.
There is a continuously increasing demand--in respect to both quality and quantity--on the part of the consumers for electric cables, wirings and components made of copper wires of high purity and excellent electric properties. It is well known from practice that pure copper is not suitable for certain purposes. As a consequence, low-alloyed copper wires are produced for special purposes where the alloying contents are between 0.05-1.5%. These alloyed copper wires are mostly used in cases, in which beside the proper electric conductivity other requirements are also to be met, as for example; where the wire is subjected to high wearing it has to be wear-resistant; where profiled work pieces are being produced, machinability is important; and where subject to high mechanical or thermal stresses, a proper tensile strength is required.
It is a well known fact that a Cu-Ag alloy of 0.05-0.1% Ag,--due to its high softening point and good creep strength after cold working--is well suitable for manufacturing commutator segments, transistor bases and welding electrodes. Due to its excellent cold working characteristics and drawability, a Cu-Sn alloy of 1.25% Sn is most suitable for the production of components for switches, fuse-elements and diaphragms. In addition to its good electric and heat conductivity, a Cu-Cd alloy has excellent tensile strength and hardness; and where such alloy has Cd content of between 0.5 and 1.5% it is the best one for use under high wearing conditions. Cu-Cd alloys are used for producing overhead lines, connections, electrodes, current conducting rings and rails. A Cu-Pb alloy with 1% Pb-content may be best suited--due to its good workability and machinability--for the production of screws, connecting elements and components of motors and switches. At last, due to its good electric conductivity, and the excellent tensile strength at high temperature and in particular, due to its workability a Cu-Zr alloy of 0.1-0.2% Zr content can be used, for collector rings, current leading axles, transformers to be operated at a high temperature, as well as for the jaws of butt welding machines.
Besides the applications and possibilities listed above further requirements are demanded for rods of diameter 8-12 mm--to be processed in high speed drawing machines at the up-to-data cable works. Such requirements are the homogenity and chemical purity of the wires. The total quantity of the undesired impurities--beyond the oxygen content and the contained alloying element--must not be more than 80 ppm. A further important requirement is that the wire must be free of all kinds of physical defects, such as inclusions, cracks and rolling defects, and at the same time the surface of the wire to be processed must be bright. Finally, a most important requirement is that the wire should be available in coils of a weight of at least 2000 kg and it should be soft and well drawable. The alloyed copper wire rods are partly produced by wire bar rolling traditionally or by continuous casting and rolling.
With the traditional technology, the alloy is produced in induction furnaces, in certain cases under vacuum or protective gases. The next phase includes the casting of the round ingots into watercooled casting moulds. After cooling, the feeder of the ingot is cut and the material needed for rolling is prepared by hot-pressing. Thereafter the rod is hot rolled to the required diameter, coiled into coils and if it is necessary the coils are pickled. In the course of the manufacturing steps previously described, the material has to be heated and cooled, respectively, in the three distinct operational phases, i.e. melting, pressing and rolling. The energy consumption needed for each of these phases, makes the production very uneconomical and the waste material formed in the process decreases the material yield as well. A further drawback of the traditional production lies in the fact that the weight of the coils produced is not more than 100 to 150 kg, which is not in compliance with the requirements of modern cable producing machines. Due to the small weight of the coils the number of the welded joints increases, resulting in a further source of defects in processing.
A further drawback lies in the fact that the surface of the wires produced is not bright and as a consequence the wire has to be pickled.
The continuous casting of rods and production of the alloyed wire rod by hot-rolling represents the most modern technology known up to now. With this technology the metal is melted in an induction furnace, thereafter the melt is cooled in a graphite die in vertically or horizontally arranged equipment. Depending on the type of the alloy the rods--generally with a diameter of 20 to 30 mm--are wound into coils weighing about 2000 Kg. After having been heated, rolled and pickled the wire coils are ready for use in cable-works. The costly technology, and the high oxygen content of the rods as well as difficulties connected with the usage of graphite dies have a negative influence on the economy and the efficiency of the production.
A technology for the production of copper wire rods of oxygen free and high purity--called dipforming process--is also known. A pure copper wire, the so-called core-wire, is driven through the molten copper, the liquid copper is cooled down, crystallizing on the surface of the core-wire, while the temperature of the core-wire is increased to the ambient temperature. After pre-cooling and hot rolling the obtained rod is cooled in a closed emulsion system and finally wound to coils weighing 2500 to 3500 kp. According to this technology a part of the energy needed for melting is used for rolling. No further heating is needed in the process. Oxygen free, high purity copper cathode of 99.99% Cu-content produced by electrolyses is the raw material of the process. The quality of the cathode is protected by a charcoal layer in the furnace system and an inert protective gas in the entire technological system.
This process, using the technology of casting rolling is a really economical continuous production of the copper wire rods. In spite of this fact it has not been applied for the production of the different alloyed copper wires. The reason for this is, that the furnace system--just to ensure the continuous casting, contains a relatively large quantity of molten metal. In producing alloyed copper wire the entire metal quantity has to be alloyed in order to obtain the necessary composition and this entire quantity will be wasted when changing alloying material. The metal contaminated by the previous alloying element has to be discharged from the system, and a charge according to the new alloying composition has to be melted.
The aim of the present invention is to develop a process for the production of alloyed copper wire of different kinds keeping all the benefits of the dip-forming process presently used for the production of oxygen free copper wire rod and making the process suitable for continuous production of alloyed copper wires in optional quantity, practically without material loss and permitting a change of alloy without influence on the production of high purity oxygen free copper wire rods.